This multiple-dose escalation study evaluates the lung-specific bioefficacy of oral administration with DMP-777 in adult patients with cystic fibrosis. The objectives are to assess the magnitude of extracellular human neutrophil elastase (HNE) inhibitory activity in BAL fluid, and to determine the correlation between the magnitude of BAL HNE inhibition and (1) improvement in biological indicies relevant to the pathogenesis of lung disease in CF and (2) improvement in a disease-specific quality of life questionnaire.